Spicules are most conspicuously present in which class?

• Correct Answer: hexactinellida
• trichina
• phylum
• spirogyra

Explanation: Take an up-close tour (http://openstaxcollege. org/l/sponge_ride) through the sponge and its cells. The presence and composition of spicules/spongin are the differentiating characteristics of the three classes of sponges (Figure 28.4): Class Calcarea contains calcium carbonate spicules and no spongin, class Hexactinellida contains six-rayed siliceous spicules and no spongin, and class Demospongia contains spongin and may or may not have spicules; if present, those spicules are siliceous. Spicules are most conspicuously present in class Hexactinellida, the order consisting of glass sponges. Some of the spicules may attain giant proportions (in relation to the typical size range of glass sponges of 3 to 10 mm) as seen in Monorhaphis chuni, which grows up to 3 m long.

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